An IC chip is electrically connected to a printed circuit board by a mounting method such as a wire bonding method, a TAB method or a flip-chip method.
In the wire bonding method, an IC chip is die-bonded to a printed circuit board by adhesive or the like, the pads of the printed circuit board are connected to the pads of the IC chip by wires such as metallic wires and then a sealing resin such as a thermosetting resin or a thermoplastic resin is applied to protect the IC chip and the wire.
In the TAB method, wires referred to as leads are connected in the block by a solder or the like and then the bumps of an IC chip and the pads of a printed circuit board are sealed by a resin.
In the flip-chip method, the pads of an IC chip are connected to the pads of a printed circuit board by through bumps and the gaps between the bumps and the respective pads are filled with a resin.
In each of these mounting methods, however, the IC chip and the printed circuit board are electrically connected to each other through lead members (wires, leads or bumps) for connection therebetween. These lead members tend to be cut off and eroded, making the connection of the printed circuit board to the IC chip cut off or causing malfunctions.
In addition, in each of these mounting methods, a sealing thermoplastic resin such as an epoxy resin is employed to protect the IC chip. However, if bubbles are contained at the time of filling the resin, then the lead members are broken, the IC pads are eroded and reliability of the IC chip is deteriorated due to the bubbles. To seal the IC chip or the like by a thermoplastic resin, it is required to create resin filling plungers and metallic molds in accordance with the respective components of the printed circuit board. Further, in case of employing a thermosetting resin, it is necessary to select a thermosetting resin in view of the materials of the lead members, a solder resist and the like, thereby disadvantageously causing cost increase..
The present invention has been made to solve the above-stated problems. It is an object of the present invention to propose a multilayer printed circuit board capable of being directly, electrically connected to an IC chip without using a lead member and a manufacturing method of the multilayer printed circuit board.
After being devoted to the intensive studies of the multilayer wiring board, the inventors of the present invention finally devised a structure capable of electrically connecting a multilayer printed circuit board to an IC chip without using-leads and a sealing resin by providing opening portions, through holes and counterbore portions in the resin insulating substrate to thereby contain an electronic component such as an IC chip therein in advance, building up a plurality of interlayer insulating layers, providing via holes on the die pads of the IC chip by photoetching or laser, forming conductor circuits serving as conductive layers, and further providing the interlayer insulating layers and the conductive layers repeatedly to thereby provide the multilayer printed circuit board.
Moreover, the inventors of the present invention devised a structure of mounting an electronic component, such as an IC chip, on the surface layer of the multilayer printed circuit board by providing opening portions, through holes and counterbore portions in the resin insulating substrate to thereby contain an electronic component, such as an IC chip, therein in advance, building up interlayer insulating layers, providing via holes on the die pads of the IC chip by photoetching or laser, then forming conductor circuits serving as conductive layers and further providing the interlayer insulating layers and the conductive layers repeatedly. With this structure, it is possible to electrically connect the multilayer printed circuit board to the IC chip in without using leads. It is also possible to mount the electronic components such as the IC chip having different functions and to obtain a multilayer printed circuit board having a greater function. To be specific, a cache memory is embedded as the IC chip included in the board and an IC chip having an operation function is mounted on the front surface of the multilayer printed circuit board, whereby it is possible to arrange the IC chip and the cache memory in proximity while separately manufacturing the cache memory having low yield and the IC chip.
Furthermore, after being devoted to the intensive studies, the inventor of the present invention devised providing opening portions, through holes and counterbore portions in resin insulating substrate to thereby contain an electronic component such as an IC chip in advance and forming a transition layer consisting of at least two-layer structure on the die pad of the IC chip. An interlayer insulating layer is provided on the transition layer and a via hole is provided on a via hole which is the transition layer of the IC chip by photo-etching or laser and a conductor circuit serving as a conductive layer. Thereafter, interlayer insulating layers and conductive layers are repeatedly built up and a multilayer printed circuit board is provided, thereby making it possible to electrically connect the multilayer printed circuit board to the IC chip without using a sealing resin and leads. Further, since the transition layer is formed on the IC chip portion, the IC chip portion is flattened. Accordingly, the upper interlayer insulating layer is flattened and the thickness thereof becomes uniform. Further, the transition layer makes it possible to maintain the stability of a shape in case of forming the via hole on the upper layer.
The reasons for providing the transition layer on the pad of the IC chip are as follows. First, if the die pad becomes fine pitch and small in size, alignment at the time of forming via holes becomes difficult. Due to this, by providing a transition layer, the alignment is facilitated. If the transition layer is provided, buildup layers can be stably formed even while a die pad pitch is 150 μm or less and a pad size is 20 μm or less. If the via hole is formed in the interlayer insulating layer with the die pad on which the transition layer is not formed and the diameter of the via is larger than the diameter of the die pad, then a polyimide layer serving as the protective layer of the surface of the die pad is dissolved and damaged at the time of removing the residue on the bottom of the via and roughening the surface of the interlayer resin insulating layer. On the other hand, if laser is applied and the via diameter is larger than the diameter of the die pad, a polyimide layer (or protective layer of the IC) is damaged by the laser. Moreover, if the die pad of the IC chip is very small and the diameter of the via is larger than the size of the die pad, then positioning becomes quite difficult even by photo-etching or laser and connection errors occur between the die pad and the via hole.
By providing the transition layer on the die pad, by contrast, it is possible to ensure connecting the via on the die pad even with a die pad pitch of 150 μm or less and a pad size of 20 μm or less, thereby improving the connection between the pad and the via and reliability. In addition, by interposing the transition layer having a larger diameter on the pad of the IC chip, the fear that the protective film of die pad and the IC are dissolved and damaged if the protective film is immersed in an acid or an etching solution in later steps such as a de-smear and plating steps or conducting various annealing steps, is eliminated.
The multilayer printed circuit board itself fulfils the functions. In some cases, BGA's, solder bumps or PGA's (conductive connection pins) may be provided to connect to a mother board or a daughter board which is an external board so as to function as a package substrate for a semiconductor device. With this constitution, wiring length and loop inductance can be reduced compared with a case of connecting the multilayer wiring board to the external board by a conventional mounting method.
Now, the transition layer defined in the present invention will be described.
The transition layer means a mediate layer provided on an intermediate portion so as to directly connect the IC chip, which is a semiconductor element, to the printed circuit board without using a conventional IC chip mounting technique. The transition layer is characterized by being formed out of two or more metallic layers or by being made larger than the die pad of the IC chip which is the semiconductor element. The transition layer thus characterized enables the enhancement of electrical connection and positioning characteristics and via hole processing by means of laser or photo-etching without damaging the die pad. This can ensure embedding and containing the IC chip in the printed circuit board, and connecting the IC chip to the printed circuit board. This also enables a metallic layer serving as the conductive layer of the printed circuit board to be directly formed on the transition layer. For example, the conductive layer is the via hole of the interlayer resin insulating layer or a through hole on the substrate.
As a resin substrate for including electronic components such as the IC chip therein used in the present invention, a substrate obtained by building up prepregs impregnated with a resin or a glass epoxy resin obtained by impregnating an epoxy resin, a BT resin, a phenol resin or the like with a reinforcement or a core material such as a glass epoxy resin. An ordinary resin substrate used for the printed circuit board may be used. Alternatively, a double-sided copper-clad laminate, a one-sided plate, a resin plate without a metallic film or a resin film may be used. However, if the resin is heated at 350° C. or higher, the resin is dissolved and carbonated. Further, ceramic cannot be used for the substrate since it is inferior in outside workability.
The IC chip is coupled to a resin insulating substrate such as a core substrate in which a cavity formed as a counterbore, a through hole or an opening for containing an electronic component such as the IC chip, by an adhesive or the like.
The entire surface of the core substrate including the IC chip is subjected to deposition, sputtering or the like, thereby forming a conductive metallic film (or first thin film layer) on the entire surface. The metal used may be tin, chromium, titanium, nickel, zinc, cobalt, gold, copper or the like. The thickness of the conductive metallic film is preferably between 0.001 and 2.0 μm. If the thickness is smaller than 0.001 μm, the conductive metallic film cannot be provided uniformly on the entire surface. It is difficult to form a conductive metallic film having a thickness exceeding 2.0 μm and even if formed, the film does not improve advantages. The thickness is more preferably between 0.01 and 1.0 μm. If chromium is used, the thickness is preferably 0.1 μm.
The first thin film layer covers the die pad, thereby making it possible to improve the adhesiveness of the transition layer and the IC chip to an interface with the die pad. Further, by covering the die pad with such a metal, it is possible to prevent the entry of moisture into the interface, to prevent the dissolution and erosion of the die pad and to improve reliability. In addition, the first thin film layer allows the connection between the multilayer printed circuit board and the IC chip by a mounting method without using leads. If using chromium, nickel or titanium, it is possible to prevent the entry of moisture into the interface and excellent metal adhesiveness is ensured. The thickness of chromium, titanium or the like is set so that the sputtered layer does not crack and that adhesiveness between the metal and the upper layer is ensured. With a reference to a positioning mark on the IC chip, a positioning mark is formed on the core substrate.
The second thin film layer is formed on the first thin film layer by sputtering, deposition or electroless plating. The metal used is exemplified by nickel, copper, gold, silver or the like. It is preferable to use copper because it has appropriate electrical characteristic and is economical and a thickening layer formed in a later step mainly consists of copper.
The reason for providing the second thin film layer is that only the first thin film layer cannot provide a electroplating lead to form a thickening layer to be described later. The second thin film layer 36 is employed as a thickening lead. The thickness of the second thin film is preferably 0.01 to 5 μm. If the thickness is smaller than 0.01 μm, the second thin film layer cannot function as a lead. If the thickness exceeds 5 μm, the lower first thin film layer is cut more than the second thin film layer to thereby generate gaps, moisture tends to enter the interference and reliability deteriorates during etching.
The second thin film layer is thickened by electroless plating or electroplating. The type of a metal formed is exemplified by copper, nickel, gold, silver, zinc, iron or the like. It is preferable to use copper for electroplating because copper has appropriate electrical characteristic, is economical, has the strength and structural resistance of the transition layer and a conductor layer to be build up in a later step mainly consists of copper. The thickness of the second thin film layer is preferably 1 to 20 μm. If the thickness is smaller than 1 μm, the connection reliability of the layer with the upper via hole deteriorates. If the thickness exceeds 20 μm, undercut occurs during etching and thereby gaps are generated in the interface between the formed transition layer and the via hole. In some cases, the first thin film layer may be directly plated to thicken the layer or multiple layers may be provided.
Thereafter, an etching resist is formed with reference to the positioning mark on the core substrate, exposure and development are performed to expose the portions of the metal other than that of the transition layer and etching is then performed, thereby forming a transition layer consisting of the first thin film layer, the second thin film layer and a thickening layer on the die pad of the IC chip.
In case of forming a transition layer by a subtractive process, a metallic film is thickened by electroless plating or electroplating. The type of the plated member to be formed is exemplified by copper, nickel, gold, silver, zinc, iron or the like. It is preferable to use copper because copper has appropriate electrical characteristic and is economical and a buildup conductive layer to be formed later mainly consists of copper. The thickness is preferably in the range of 1 to 20 μm. If the thickness exceeds the range, undercut occurs during etching and gaps may be generated in the interface between the transition layer and the via hole to be formed. Thereafter, an etching resist is formed, exposure and development are performed to the portion of the metal other than that of the transition layer, thereby forming a transition layer on the pad of the IC chip.
As stated above, the inventors of the present invention devised including an IC chip in a package substrate by containing the IC chip in a recess formed in the core substrate and building up an interlayer resin insulating layer and a conductive circuit on the core substrate.
According to this method, a metallic film is formed on the entire surface of the core substrate containing the IC chip so as to cover or protect the pad of the IC chip, or, in some cases, forming a transition layer on the pad, thereby electrically connecting the pad to the via hole of the interlayer resin insulating layer.
However, since the metallic film is formed on the entire surface, a positioning mark formed on the IC chip is concealed and a mask on which wirings are drawn or a laser device cannot be positioned relative to the substrate. Due to this, it is estimated that a positional error occurs between the pad on the IC chip and the via hole and that electrical connection cannot be established between the pad and the via hole.
The present invention has been made to solve the above-stated problems. It is another object of the present invention to propose a method of a multilayer printed circuit board manufacturing method capable of being appropriately connected to an IC chip included in the multilayer printed circuit board.
Accordingly, a method of manufacturing a multilayer printed circuit board having interlayer insulating layers and conductor layers repeatedly formed on a substrate, via holes formed in the interlayer insulating layers, and establishing electrical connection through the via holes, is characterized by comprising at least the following steps (a) to (c):    (a) containing an electronic component in said substrate;    (b) forming a positioning mark on said substrate based on a positioning mark of said electronic component; and    (c) conducting working or formation based on the positioning mark of said substrate.
Accordingly, a positioning mark is formed on a substrate containing an electronic component therein based on the positioning mark of the electronic component, and working or formation is conducted based on the positioning mark of the substrate. Due to this, it is possible to form a via hole in an interlayer resin insulating layer on the substrate so as to accurately match the position of the via hole to the position of the electronic component.
Working in this case means the IC chip which is the electronic component or all that formed on the substrate. For example, a transition layer on the pad of the IC chip, a recognized character (e.g., an alphabet, number or the like), a positioning mark are included.
Also, formation in this case means all that formed on the interlayer resin insulating layer (which does not contain a reinforcement such as glass cloths) provided on the core substrate. For example, a via hole, a wiring, a recognized character (e.g., an alphabet, number or the like), a positioning mark and the like are included.
Accordingly, a method of manufacturing a multilayer printed circuit board having interlayer insulating layers and conductor layers repeatedly formed on a substrate, via holes formed in the interlayer insulating layers, and establishing electrical connection through the via holes, is characterized by comprising at least the following steps (a) to (d):    (a) containing an electronic component in said substrate;    (b) forming a positioning mark on said substrate based on a positioning mark of said electronic component by using laser;    (c) forming a metallic film on the positioning mark of said substrate; and    (d) conducting working or formation based on the positioning mark of said substrate.
Accordingly, a positioning mark is provided on a substrate containing an electronic component therein by laser based on the positioning mark of the electronic component, working or formation is conducted based on the positioning mark of the substrate after forming a metallic film on the positioning mark provided by laser. Due to this, it is possible to form a via hole in the interlayer insulating layer on the substrate so as to accurately match the position of the via hole to the position of the electronic component. In addition, since the metallic film is formed on the positioning mark provided by laser, it is possible to easily recognize the positioning mark by a reflection method and to conduct accurate positioning.
Accordingly, a method of manufacturing a multilayer printed circuit board having interlayer insulating layers and conductor layers repeatedly formed on a substrate, via holes formed in the interlayer insulating layers, and establishing electrical connection through the via holes, is characterized by comprising at least the following steps (a) to (e):    (a) containing an electronic component in said substrate;    (b) forming a positioning mark on said substrate based on a positioning mark of said electronic component by using laser;    (c) forming a metallic film on the positioning mark of said substrate;    (d) forming the interlayer insulating layers on said substrate; and    (e) processing or forming via hole openings in said interlayer resin insulating layers based on the positioning mark of said substrate.
Accordingly, a positioning mark is formed on a substrate containing an electronic component therein based on the positioning mark of the electronic component, working or formation is conducted based on the positioning mark of the substrate after forming a metallic film on the positioning mark. Due to this, it is possible to form a via hole in an interlayer insulating layer on the substrate so as to accurately match the position of the via hole to the position of the electronic component. In addition, the metallic film is formed on the positioning mark provided by laser. Due to this, even if an interlayer insulating layer is formed on the positioning mark, the positioning mark can be easily recognized and accurate positioning can be conducted by recognizing an image by a reflection method.
As described above, the inventor of the present invention devised a structure capable of establishing electrical connection between a multilayer printed circuit board and an IC chip without using a sealing resin, leads or bumps by providing an opening portion, a through hole or a counterbore portion in a resin insulating substrate to include an electronic component such as an IC chip therein, building up interlayer resin insulating layers, providing a via on the pad of the IC chip by photo-etching or laser, forming a conductor circuit serving as a conductive layer, repeatedly providing the interlayer insulating layers and the conductive layers and thereby forming the multilayer printed circuit board.
However, since the pad of the IC chip is normally formed out of aluminum or the like, the pad is oxidized in manufacturing steps and an oxide film is formed on the surface of the pad. Due to this, it was discovered, the oxide film formed on the surface causes an increase in the connection resistance of the pad and, the multilayer printed circuit board cannot be appropriately electrically connected to the IC chip. It was also discovered that if an oxide film remains on the die pad, the adhesiveness between the pad and the transition layer becomes insufficient and reliability cannot be satisfied.
The present invention has been made to solve the above-stated problems. It is a still further object of the present invention to propose a multilayer printed circuit board capable of being appropriately electrically connected to an IC chip without leads and a method of manufacturing the multilayer printed circuit board.
Accordingly, in order to achieve the above purpose, a method of manufacturing a multilayer printed circuit board is characterized by comprising at least the following steps (a) to (e):    (a) containing an electronic component in said substrate;    (b) removing a film on a surface of a die pad of said electronic component;    (c) forming a transition layer to be connected to a via hole of a lowermost interlayer insulating layer, on said die pad;    (d) forming the interlayer insulating layers on said substrate; and    (e) forming the via holes connected to the conductor circuits and the transition layers, in said interlayer resin insulating layers.
Accordingly, since an IC chip is contained in a substrate, the multilayer printed circuit board can be electrically connected to the IC chip without leads. Besides, an oxide film removal process is conducted to the connection surface of the die pad of an electronic component such as an IC chip, it is possible to reduce the electrical resistance of the die pad and to improve electrical conductivity thereof. Further, by proving a transition layer on an IC chip portion, the IC chip portion is flattened. Due to this, the interlayer insulating layer on the IC chip is also flattened and film thickness becomes uniform. Furthermore, if a via hole on an upper layer is formed, it is possible to maintain the stability of shape. It is preferable that the film is completely removed.
Accordingly, by completely removing the oxide film by one of inverse sputtering and a plasma process, it is possible to improve the electrical conductivity of the die pad of the IC chip.
In case of inverse sputtering, inactive gas such as argon gas is used as sputtering gas and inverse sputtering is conducted to the oxide film on the surface of the die pad, thereby completely removing the oxide film. In case of the plasma process, the substrate is put in a device in a vacuum state, plasmas are discharged in oxygen or nitrogen, carbon dioxide and carbon tetrafluoride to thereby remove the oxide film on the surface of the die pad.
Accordingly, the film removal and the formation of the lower most layer of the transition layer are conducted under a non-oxygen atmosphere in succession. Due to this, it is possible to improve the electrical conductivity and adhesiveness between the die pad of the IC chip and the transition layer without forming an oxide film on the surface of the pad again.
Accordingly, a multilayer printed circuit board having interlayer insulating layers and conductor layers repeatedly formed on a substrate, via holes formed in the interlayer insulating layers, and establishing electrical connection through the via holes, is characterized in that                an electronic component is included in said substrate;        a transition layer to be connected to a via hole of a lowermost interlayer insulating layer is formed on a die pad of said electronic component; and        a film on a surface of said die pad is removed.        
Accordingly, since the IC chip is contained in the substrate, the multilayer printed circuit board can be electrically connected to the IC chip without leads. Further, since an oxide film removal process is conducted to the connection surface of the die pad of an electronic component such as an IC chip, it is possible to reduce the electrical resistance of the die pad and improve the electrical conductivity thereof. Further, by providing the transition layer on the IC chip portion, the IC chip portion is flattened. Due to this, the interlayer insulating layer on the IC chip is also flattened and film thickness becomes uniform. In addition, even if a via hole on the upper layer is formed, it is possible to maintain the stability of shape. It is preferable that the film is completely removed.